1. Field of the Invention
The present invention relates to a microetching composition useful for treating surfaces of copper or copper alloys.
2. Description of the Background Art
In the manufacture of printed-wiring boards, copper surfaces are polished prior to coating such surfaces with an etching resist or a solder resist to improve adhesion of these resists to the copper surfaces. Mechanical cleaning using a buffing or scrubbing machine, or chemical cleaning, known as microetching, are used for roughening the copper surfaces. Microetching is more popular for treating substrates with fine line patterns. The copper surface is etched as deeply as 1-5 .mu.m by the microetching treatment. This depth of etching is calculated from the weight of copper decreased by etching, the specific gravity, and the surface area of the copper.
A microetching agent used for the microetching process which contains a cationic surfactant such as a quaternary ammonium salt is disclosed in U.S. Pat. No. 4,956,035. The specification of this USP states that the microetching agent can smooth the surface of a metal and improve adhesion of an etching resist to the surface.
However, the smooth surface treated with the microetching agent does not exhibit adequate adhesion with a prepreg, or a curable ink in which a hard (highly cross-linked) resin is used. The adhered portion may peel or produce swelling, which may permit chemical solutions to invade the space between the metal surface and the resin in the subsequent chemical treatment steps.
The inventors of the present invention have undertaken extensive studies and found that a microetching agent comprising a small amount of a polymer compound which contains polyamine chains or a cationic group, or both, can produce a deep irregularly etched surface on the surface of copper or a copper alloy. This surface differs from the surface obtained by treatment with the above-described microetching agent disclosed by U.S. Pat. No. 4,956,035 and exhibits excellent adhesion to a solder resist and the like.